City of Prince George - Snow Disposal at the Lansdowne Road ...

5.0 DISCUSSION
CITY OF PRINCE GEORGE
SNOW DISPOSAL STUDY AT
THE LANSDOWNE ROAD WASTEWATER TREATMENT CENTRE
5.1 Effect of Snow Disposal on WWTC Effluent Quality
The discharge limits at the WWTC under the present permit are 65 mg/L for BOD5 and 50
mg/L for TSS. Future permit limits after the WWTC upgrade are likely to be maximum
concentrations of 45 mg/L for both BOD5 and TSS, and average concentrations of 30 mg/L for
BOD5 and TSS. There are no discharge limits for ammonia or metals specified in the permit.
As shown in Table 1, the snow additions to the chlorine chamber resulted in a significant
lowering of the average temperature of the WWTC effluent from 11.1 C to 5.4 C. The snow
additions resulted in significant increases in the WWTC effluent average BOD5 concentration
from 41 mg/L to 46 mg/L, and in the effluent average TSS concentration from 11 mg/L to 56
mg/L. The effluent pH and conductivity were marginally increased, and ammonia
concentration was unaffected.
Of the water quality parameters listed in Tables 1 and 2, TSS is the only one likely to limit
snow melting from the standpoint of effluent discharge limits under the existing permit. The
TSS concentrations in the eight grab samples of chlorine chamber effluent ranged as high as 85
mg/L, well over the permit maximum of 50 mg/L. Under present and future permitted
discharge limits for TSS, the solids content of the snow will be the water quality parameter
which limits melt volumes. The impact of effluent TSS on the snow melting capacity of the
WWTC is discussed in Section 5.3.
The BOD5 of the effluent was increased by 5 mg/L to 49 mg/L in the composite sample, a
concentration which is well under the existing permit maximum of 65 mg/L, and slightly over
the future permit value of 45 mg/L. However, the expansion/upgrade now in progress at the
WWTC is designed to improve process BOD5 removal to effluent concentrations of 20 mg/L,
so an increase of 5 mg/L due to snow additions should not be a concern. A possible source of
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